Many chemicals are well known for skin whitening activities, as hydroquinone, kojic acid, arbutin and ascorbic acid derivatives. However, the safety, stability, smell, or efficacies of these whitening agents do not satisfy consumers needs.
WO 02/053121 (LG Household & Healthcare Company) discloses glucose- and sucrose-esters with fatty acids having a carbon chain length of C3 to C6 and their use in cosmetics for skin whitening. WO 03/074013 and EP 1 340 486 A1 (Cognis France S. A.) discloses the use of sugar fatty acid esters as inhibitors of the melanin synthesis in hair and skin cells.
When trying to achieve a highly effective skin whitening activity in a cosmetic composition, the use of fatty acid esters is limited due to their emulsifying properties. Thus with sugar fatty acids the skin whitening activity that can be achieved in standard cosmetic formulations is limited.
WO 98/55087 (Laboratories Serobiologiques) describes cosmetic compositions comprising an extract from Waltheria indica. The anti-UV A, anti-UV B and the anti-collagenase effects, anti-ageing, anti-elastase, anti-radical and glutathione auto-synthesis reducing activity are disclosed. WO 01/056541 (=EP 1 253 906 B1) (Cognis France S. A.) describe cosmetic compositions containing extracts of Waltheria indica in combination with ferulic acid. WO 01/056541 discloses that these mixtures can be used as skin whiteners and as tyrosinase inhibitors, it does not disclose that Waltheria indica extracts alone, or in combination with any other component, display tyrosinase inhibiting activity in melanocytes (i.e. acting through a decrease of cellular tyrosinase activity and not as direct tyrosinase inhibitors).
It is preferred that skin whitening cosmetic compositions themselves are white or of a very light colour. When trying to achieve a highly effective skin whitening activity in a cosmetic composition, the use of plant extracts is limited due to the colour of the plant extracts.
Aim of the invention was to provide a skin whitening active which overcomes the draw-backs of the prior art. Of special interest was that a highly effective skin whitening active can be easily incorporated into cosmetic composition e.g. without developing or adjusting the emulsifier system for each formulation; e.g. not to contribute to the colour of the final formulation; e.g. not to require a concentration which interferes with the formulation of the cosmetic composition, thus being highly effective at low concentrations. In addition it is desired that the skin whitening active does not or only to a much lower extend than products known in the market, cause an irritation of the skin onto which it is applied.
It has surprisingly be found, that the skin whitening active of the invention can be formulated at a highly efficient concentration in cosmetic compositions. It has been found the skin whitening active can be easily formulated into a broad range of cosmetic compositions (e.g. W/O emulsions, O/W emulsions) and that it—at the same time—leads to very lightly coloured, in some cases even colour-less end products. In addition the skin whitening active of the invention does not show any irritation on the skin.
The skin whitening actives according to the invention allow to formulate cosmetic compositions which are highly effective in skin whitening, show very little colour and can be formulated in a wide range of cosmetic formulations types, e.g. W/O emulsions or O/W emulsions without special requirement to the emulsion system.